A composite for preventing ice adhesion or for facilitating the removal of ice, snow, and frozen contaminants is desirable. The application fields are very broad, encompassing critical areas such as aircraft, vehicles, marine, wind turbine, and electric power cables. For example, in the absence of ice nuclei, supercooled water droplets will remain in the liquid form down to −40° C., such as in stratiform and cumuli clouds. Flying though such clouds, aircraft will seed these droplets, causing abrupt icing on exposed surfaces. In-flight icing causes many tragic accidents.
Anti-icing method utilizing freezing-point depressant solution absorbed into a hydrophilic 50% porous polymer matrix are known in the art, such as U.S. Pat. No. 8,221,847, among others. Many low surface energy materials, such as silicon-containing polymers [1], fluoropolymers [2] and their composites are claimed as anti-icing coatings, examples include: U.S. Pat. No. 8,202,620, U.S. Pat. No. 8,193,294, U.S. Pat. No. 7,897,667, U.S. Pat. No. 7,915,371, U.S. Pat. No. 7,910,683, U.S. Pat. No. 7,261,768, U.S. Pat. No. 7,261,768, U.S. Pat. No. 7,202,321, U.S. Pat. No. 6,809,169, U.S. Pat. No. 6,797,795, U.S. Pat. No. 6,733,892, U.S. Pat. No. 6,579,620, U.S. Pat. No. 6,432,486, U.S. Pat. No. 6,395,345, U.S. Pat. No. 6,363,135, U.S. Pat. No. 6,183,872, U.S. Pat. No. 6,153,304, U.S. Pat. No. 6,114,448, U.S. Pat. No. 6,084,020, U.S. Pat. No. 6,068,911, U.S. Pat. No. 5,904,959, U.S. Pat. No. 5,747,561, U.S. Pat. No. 5,736,249, U.S. Pat. No. 5,336,715, U.S. Pat. No. 5,188,750, U.S. Pat. No. 5,187,015, U.S. Pat. No. 5,075,378, U.S. Pat. No. 5,045,599, U.S. Pat. No. 5,008,135, U.S. Pat. No. 4,565,714, and U.S. Pat. No. 4,301,208.
The NASA Lewis Research Center, which operates the world's largest refrigerated Icing Research Tunnel (IRT), has performed icing research for over 50 years. The studies conducted by NASA [3] and other researchers have concluded that fluoropolymers, siloxane resins, their composites, as surface coatings are inadequate for anti-icing applications [3]. For example, repeated ice removal or rain erosion is shown to increase ice adhesion on silicone surfaces [3].
Superhydrophobic nano-micron hierarchical structures of lotus leaves have been studied since 1977 [5]. Various approaches for mimicking the surface topography and surface chemistry of lotus leaves have been attempted, resulting in the launch of biommimetic products [6]. The main methods developed so far have been: 1) layer-by-layer assembly, 2) polymer film roughening, 3) chemical vapor deposition, 4) sol-gel process, 5) phase separation, 6) hydrothermal synthesis, and 7) coating with composites of nanoparticles. The following are typical examples of US patents that are related to superhydrophobic coatings: U.S. Pat. No. 8,241,508, U.S. Pat. No. 8,236,379, U.S. Pat. No. 8,216,674, U.S. Pat. No. 8,211,969, U.S. Pat. No. 8,202,614, U.S. Pat. No. 8,187,707, U.S. Pat. No. 8,153,233, U.S. Pat. No. 8,147,607, U.S. Pat. No. 8,137,751, U.S. Pat. No. 8,067,059, U.S. Pat. No. 8,043,654, U.S. Pat. No. 8,017,234, U.S. Pat. No. 7,998,554, U.S. Pat. No. 7,985,475, U.S. Pat. No. 7,985,451, U.S. Pat. No. 7,968,187, U.S. Pat. No. 7,943,234, U.S. Pat. No. 7,914,897, U.S. Pat. No. 7,754,279, U.S. Pat. No. 7,722,951, U.S. Pat. No. 7,704,608, U.S. Pat. No. 7,695,767, U.S. Pat. No. 7,485,343, U.S. Pat. No. 7,419,615, U.S. Pat. No. 7,291,628, U.S. Pat. No. 7,258,731, U.S. Pat. No. 7,253,130, U.S. Pat. No. 7,211,605, U.S. Pat. No. 7,150,904, U.S. Pat. No. 6,743,467, U.S. Pat. No. 6,649,222, U.S. Pat. No. 3,391,428
However, superhydrophobic surfaces do not always show low ice adhesion properties. Secondly, their anti-icing properties deteriorate from repeated icing/de-icing cycles due to the destruction of very thin and fragile nano/micron hierarchical structures. Thirdly, prolonged exposure to high humidity levels leads to high ice bonding forces due to ice forming in and getting trapped into inter-asperity spaces [4]. Other factors, such as technical complexity of production and scale-up difficulties hinder application in the real world.